1. Field of the Invention
The present invention relates in general to the fabrication of golf clubs. More particularly, it relates to a method of making golf clubs of thermoplastic composite material.
2. Description of the Related Arts
Composite golf clubs are conventionally made of thermosetting composite material such as epoxy resin/carbon fiber prepreg. Two major methods are employed for making thermosetting golf clubs, which are: (a) the tape rolling method; and (b) the filament winding method.
The tape rolling method for making a thermosetting golf club will now be described by referring to the flow chart of FIG. 1. Epoxy resin/carbon fiber prepreg 100 is wrapped around a mandrel 102 by assistance of a rolling machine (a1). After the wrapping, the mandrel is further wound with longitudinally and latitudinally oriented polypropylene (OPP) tapes (a2), and then heated to 80-150.degree. C. for about 1-3 hours (a3). While the OPP tapes shrinks during the heating, the wrapping prepreg is compressed and hardened to form a compact tubular body. After releasing the OPP tapes (a4), the tubular body is shaped into an appropriate size (a5), and finally, its outer peripheral surface is polished (a6) and painted (a7) to produce a golf club 104.
As to the filament winding method, referring to FIG. 2, the procedures are largely the same except that the composite materials are wrapped around the mandrel in a different manner. The raw material of carbon fiber 200 is first wetted with liquid epoxy resin 202 (b1), and then the resin-covered fiber is wound around the mandrel in a spiral orientation (b2). Afterwards, the same procedures of the OPP winding, heating, OPP releasing, and so forth (b3-b8), are repeated to complete a golf club product 204.
The thermosetting golf clubs thus produced, however, do not have excellent plasticity and, in view of the fact that the thermosetting materials such as epoxy resin cannot be easily recycled, are potential sources of environment pollution. On the other hand, thermoplastic materials are easy-recycle and have excellent shock-absorbing and elastic features. Therefore, the future trend is to make golf clubs of thermoplastic materials. In recent years, polyphenylene sulfide (PPS) and nylon have been considered the most preferable materials for making thermoplastic golf clubs. There have been numerous attempts to make golf clubs of thermoplastic materials; see for example, U.S. Pat. No. 5,198,058.
Methods for making thermoplastic golf clubs can also be classified into the tape rolling method, and the filament winding method. The processes are basically the same as those for making thermosetting golf clubs, except that heat-resistant shrink tapes are used to replace the OPP tapes because the subsequent heating will take place at a much higher temperature (0-80.degree. C. above the crystalline point or softening point of the thermoplastic material.) The crystalline melting points (Tm) of nylon 6 and PPS are 225.degree. C. and 278.degree. C., respectively, whereas that of OPP is only 160.degree. C. Apparently, OPP tapes cannot be processed at such high temperatures, and a substitute having better heat resistance is thus required for making thermoplastic golf clubs. A silicon rubber tape is satisfactory for this demand when making nylon 6 golf clubs. However, because the silicon rubber tape is bound to decompose at above 290.degree. C., it is not qualified for making PPS golf clubs.
The golf clubs produced by using the silicon rubber tapes as shrink tapes generally have spiral mark defects, and as a result, the golf clubs suffer from insufficient strength and rigidity. Also, the silicon rubber tape is high-cost and is made of thermosetting materials which cannot be easily recycled.